Process for applying a layered structure on a lens

Abstract

This invention relates to an improvement for applying a layered structure onto a convex surface of a lens. After thermoforming the layered structure, a curvature direction of the layered structure is inverted. The structure is then applied on the lens surface by continuously pushing the structure against the lens surface, starting from a contact point between a convex surface of the structure and the convex surface of the lens. The curvature direction of the layered structure is then inverted again, so that it recovers the curvature direction that resulted from thermoforming. Stresses within the layered structure are then reduced, and the structure can be assembled with the lens without defects.

What is claimed is: 
     
       1. Process for applying a layered structure on a convex surface of a lens, wherein the lens is an ophthalmic lens and the layered structure includes a circular-polarizing layer efficient for at least one wavelength of visible light, the process comprising the following steps:
 /a/ providing the layered structure with a planar shape; 
 /b/ thermoforming the layered structure so that it becomes curved with a first surface being concave and a second surface being convex; 
 /c/ inverting the curvature of the layered structure so that said first surface turns convex and said second surface turns concave; 
 /d/ bringing the first surface of the layered structure in contact with the convex surface of the lens at an initial contact point; and 
 /e/ starting from the initial contact point, applying the first surface of the layered structure against the convex surface of the lens via pressure applied on the second surface of the layered structure, the first and second surfaces of the layered structure turning back to concave shape and convex shape, respectively, at a peripheral border of an increasing contact zone. 
 
     
     
       2. Process according to  claim 1 , wherein the layered structure including the circular-polarizing layer is suitable for the lens such that after step /e/ the lens is capable of filtering a light based on a circular polarization of said light. 
     
     
       3. Process according to  claim 1 , wherein step /e/ is carried out so that substantially no pressure is applied on the second surface of the layered structure out of the increasing contact zone. 
     
     
       4. Process according to  claim 1 , wherein step /e/ is carried out with the layered structure heated. 
     
     
       5. Process according to  claim 4 , wherein a temperature of the layered structure is equal or at least 75° C. during step /e/. 
     
     
       6. Process according  claim 1 , wherein the surface lens has a curvature radius below 305 millimeters, preferentially below 100 millimeters, and particularly less than 75 millimeters. 
     
     
       7. Process according  claim 1 , wherein steps /d/ and /e/ are carried out with an adhesive layer provided between the convex surface of the lens and the first surface of the layered structure. 
     
     
       8. Process according to  claim 7 , wherein the adhesive layer is applied on the convex surface of the lens and/or on the first surface of the layered structure. 
     
     
       9. Process according to  claim 7 , wherein the adhesive layer comprises a material of pressure-sensitive adhesive type. 
     
     
       10. Process according to  claim 1 , wherein pressure is applied on the second surface of the layered structure during step /e/ via a resilient membrane being inflated and pressing on the second surface of the layered structure within the increasing contact zone. 
     
     
       11. Process according to  claim 1 , wherein step /b/ is carried out so that, between steps /b/ and /c/, a curvature of the layered structure at least one point in the first surface of said layered structure is greater than or equal to a curvature of the convex surface of the lens at a point in said convex surface of the lens which corresponds to said at least one point in the first surface of the layered structure after step /e/. 
     
     
       12. Process according to  claim 11 , wherein the convex surface of the lens has a constant curvature, and wherein step /b/ is carried out so that, between steps /b/ and /c/, the layered structure has a curvature greater than or equal to the curvature of the convex surface of the lens at any point in the first surface of the layered structure. 
     
     
       13. Process according to  claim 11 , wherein the lens is of progressive addition type and the lens has curvature at a near vision point higher than a curvature of said convex surface of the lens at a far vision point, and wherein step /b/ is carried out so that, between steps /b/ and /c/, the layered structure has a curvature greater than the curvature of the convex surface of the lens at the far vision point. 
     
     
       14. Process according to  claim 1 , wherein the circular-polarizing layer comprises a quarter-wave retarding layer and a linear-polarizing layer, with a slow axis of said quarter-wave retarding layer and a polarization axis of the linear-polarizing layer forming an angle comprised between 42 and 48 degrees, or between 132 and 138 degrees, and the layered structure being oriented in steps /d/ and /e/ so that light impinging onto the convex surface of the lens passes first through the quarter-wave retarding layer and then the linear-polarizing layer. 
     
     
       15. Process according to  claim 14 , wherein the layered structure comprises the following layer sequence: protective film/linear-polarizing layer/protective film/adhesive film/quarter-wave retarding layer. 
     
     
       16. Process according to  claim 1 , wherein the layered structure further comprises at least one functional coating on said second surface of the layered structure. 
     
     
       17. Process according to  claim 15 , wherein the protective films are derived from cellulose triacetate. 
     
     
       18. Process according to  claim 15 , wherein the protective films have a thickness in the range of 75 to 85 micrometers. 
     
     
       19. Process according to  claim 15 , wherein the linear-polarizing layer is PVA-derived. 
     
     
       20. Process according to  claim 19 , wherein the linear-polarizing layer has a thickness in the range of 25 to 50 micrometers. 
     
     
       21. Process according to  claim 14 , wherein the quarter-wave retarding layer is derived from material selected from a set of materials including polycarbonate, cyclo-olefins polymers and co-polymers, norbornene, polyamide, polymethylmethacrylate (PMMA), polyethyleneterephtalate (PET), cellulose-triacetate (TAC) and cellulose acetate-butyrate (CAB). 
     
     
       22. Process according to  claim 21 , wherein the quarter-wave retarding layer has a thickness in the range of 10 to 200 micrometers. 
     
     
       23. Process according to  claim 22 , wherein the quarter-wave retarding layer comprises polycarbonate having a thickness in the range of 50 to 100 micrometers.